1. Field of the Invention
The present invention relates to a universal joint for connecting two tubular members through which fluid is passed
2. Description of the Prior Art
A first conventional universal joint is shown in FIG. 7. The universal joint 200 comprises a plug member 201 whose one end is connected with a horse or socket (not shown), an intermediate tubular member 203 whose one end is rotatably connected through ball bearings 204 with the plug member 201 and a sleeve member 202 which is at its one end connected through ball bearings 205 with the other end of the intermediate member and at the other end connected with an instrument of an air tool and so on (not shown).
An axis G1 of one end of the intermediate tubular member 203 is inclined at an angle to axes G2 and G3 of the plug and sleeve members 201 and 202, which are in alignment with one another.
The plug member 201 is universally moved relative to the sleeve member 202 at the angle formed between axes of the plug and intermediate tube members by rotating the plug member 201 relative to the intermediate tubular member 203.
A second conventional universal joint is shown in FIG. 8. The universal joint 300 comprises an intermediate tubular 301, a plug member 305 connected with the intermediate tubular member 301 and a sleeve member 307 connected with the intermediate tubular member 301. The intermediate tubular member 301 has at its opposite ends first and second outer spherical parts 302 and 303.
One end of the plug member 305 is provided with an inner spherical surface 304 in which the first outer spherical part 302 is inserted to move universally the plug member relative to the intermediate tubular member and one end of the sleeve member 307 is provided with an inner spherical surface 306 in which the second outer spherical part 303 is inserted so as to move universally the sleeve member relative to the intermediate tubular member.
Accordingly, axes G4 and G5 of the plug and sleeve members 305 and 307 can be mutually relatively changed in any angles by rotating the plug member or sleeve member.
As a third conventional universal joint, there is known a universal joint disclosed in Japanese Laid-Open Publication 4-236884.
As shown in FIG. 9, the universal joint 400 comprises an intermediate tubular member 403, first and second tubular members 401 and 402 connected with the intermediate tubular member 403 and a cover 404 surrounding the intermediate tubular member 403 between the first and second tubular members 401 and 402.
The intermediate tubular member 403 has at its opposite ends first and second outer spherical parts 403a and 403b. 
One end 401a of the first tubular member 401 is provided with an inner spherical surface 401b in which first outer spherical part 403a is inserted so as to move universally the first tubular member 401 relative to the intermediate tubular member 403 and one end 402a of the second tubular member 307 is provided with an inner spherical surface 402a in which the second outer spherical part 403b is inserted so as to move universally the second tubular member relative to the intermediate tubular member.
The cover is attached to the ends 401a and 402a of the first and second tubular members 401 and 402 and acts to prevent any dirt from entering in a space between the first and second tubular members 401 and 402. The cover is made of a flexible material such as rubber to expand and contract. The cover is adapted to expand and contract following to the universal movement of the first and second tubular members as shown in FIG. 9(b).
However, in the first conventional universal joint as shown in FIG. 7, it is necessary to rotate the plug member 201 in any direction in order to change axes of the plug and sleeve members in a desire angle. Accordingly, the handling is not very good.
In the second conventional universal joint as shown in FIG. 8, since the opposite ends of the intermediate tubular member 301 are moved universally, the axes G4 and G5 are not stable. Consequently, for example, when a horse or socket is connected with the plug member 305, the connection is difficult since the axis G4 is deviated.
In the third conventional universal joint as shown in FIG. 9, since the cover 404 is adapted to expand and contract in accordance with the universal movement of the first and second tubular members, it is easy to deform, sometimes, is destroyed or removes from the first and second tubular members. When the horse or the like is connected with the first and second tubular members, there is a possibility that the cover is gripped by hands of a user or contacts with any instrument so that the cover is destroyed and removed from the first and second tubular members. If the cover is removed from the first and second tubular members, the dirt or the like enters through the space between the first and second tubular members in the joint to lose function of sealing.